1. Field of the Invention
The present invention is in the field directed to components of furnaces used for manufacturing semi-conductors, integrated circuits and the like. More specifically, the present invention is directed to a vestibule block which is surface treated so as to generate virtually no particulate matter during normal use, and to the process of making such a surface treated vestibule block.
2. Brief Description of the Prior Art
The process of manufacturing semi-conductors integrated circuits and the like includes one or more steps where wafers of silicon are heated in a furnace while exposed to certain gases which bring about desired chemical/and physical transformation on the surface of the wafers. For example, certain gases which contain boron or arsenic are admixed with a suitable inert gas and are introduced into the furnace where they decompose and deposit certain desired elements (such as elemental boron or arsenic) on the surface of the wafers. As is well known in the art, the presence of trivalent boron or pentavalent arsenic in the tetravalent silicon material is principally responsible for the desired electrical characteristics of these devices. During the above-mentioned and like manufacturing processes (such as oxidation, polycrystalline and amorphous silicon deposition and the like) the silicon wafers are deposited and held in a suitable quartz tube, which is commonly called "diffusion tube" in the trade. Walls of the furnace are usually made of refractory or ceramic material. Typically, holes or openings are provided in two oppositely disposed walls of the furnace, and a substantially cylindrical body having a step down section, is inserted into these holes. The substantially cylindrical body having the step down section is known in the art as a "vestibule block". The vestibule block itself has an inner annulus into which the diffusion tube is placed. For a long time it was the practice in the prior art to place packing material of rock wool or glass wool around the diffusion tube to close the gap between the annulus of the vestibule block and the diffusion tube and to align the diffusion tube within a heating coil which is in the furnace. A serious disadvantage of this practice was that rock wook or glass wool generates dust (particles), which has a deletorious effect on the manufacturing process.
More specifically, as is well known in the art, the semi-conductor manufacturing process must be performed in as particle-free environment as possible. This is because the semi-conductors and integrated circuits which have been contaminated by inadvertent deposit of particles on the silicon wafers during the manufacturing process are usually defective. This disadvantage of using rock wool or glass wool for packing material has been overcome by my invention described in U.S. Pat. No. 4,278,422, in accordance with which a heat withstanding support collar is placed around the diffusion tube and within the opening of the vestibule block. Thus, the above-mentioned diffusion tube support collar of U.S. Pat. No. 4,278,422 represented a major success in the industry's efforts to reduce defects due to dust or particles in the semi-conductor manufacturing process. The state-of-the-art nonetheless continues to experience problems with dust or particulate matter which abrades from the vestibule block and/or the ceramic or refractory walls of the furnace itself. In other words, particles generated by abrasion of the vestibule blocks and/or of the walls of the furnace during the manufacturing process still cause a certain number of defective semi-conductors. The present invention is intended to eliminate or at least minimize the just-noted problem.
As still further background to the present invention the following U.S. Pat. Nos., which are directed to the composition, construction or treatment of furnaces and furnace walls, are of interest: 4,943,234, 4,656,146, 4,279,845, 4,253,417, 4,191,528, 4,105,492, 3,878,005, 3,669,640, 3,449,084, 2,438,559.